Blow-molding apparatus

ABSTRACT

Blow-molding apparatus for the fabrication of hollow bodies from thermoplastic material, wherein a pre-cast element positioned on a blow pipe receives its finished shape in a hollow mold by blowing compressed air through the pipe.

BACKGROUND OF THE INVENTION

Fabrication of plastic articles by blow-molding is used for one-time useor disposable packaging material. The complete fabrication procedure iscarried out in different, consecutive, continuous steps. In this knownprocedure, the formation of the blank on the blow pipe and the blowingof the blank itself takes only a relatively short time, but the coolingof the blown-up body within the mold takes considerably longer andabsorbs the larger part of the cycle time during the fabrication of thehollow body. The time relationship, within certain limits, depends onthe material used, on the shape of the hollow body, and on its wallthickness. With this type of operation procedure, a relatively longcycle time exists before the blow pipe is again free for the nextmolding operation, because the blow pipe is used without interruptionduring the entire fabrication procedure.

During the blow-molding of bottles with an inside protective layer of adifferent material than that of the rest of the bottle, it is well knownto place the protection layer on the blow pipe first inside a so-called"conditioning chamber" in the shape of a pre-cast form which the hollowbody is later formed. Thereafter, the blow pipe with the protectionlayer or pre-cast is brought into an injection molding device, in whichthe plastic material is placed around the blow pipe, is positionedunderneath the mold station, the two halves of the blow mold beingarranged concentrically of the conditioning chamber. After the injectionprocedure, the conditioning chamber and the blow pipe with the two-layerproduct is displaced upwardly in the axial direction until it ispositioned at the same height as the blow mold which has been previouslyconcentric to the conditioning chamber. Thereafter, the blow mold isclosed for the blowing operation. With this arrangement and with theseoperating conditions, the conditioning chamber, the blowing device, themold, and the injection device are arranged axially in a vertical line.When the hollow body has been blown up, the blow pipe is removed fromthe blow mold and inserted into the conditioning chamber, where theprotection layer is placed onto the blow pipe for the next hollow body.The pressure inside the hollow body is maintained by compressed airwhich is introduced through a hole at the side into the closed unitformed by the housing and the extrusion injection device. In order notto influence the application of the protection layer to the blow pipe,the conditioning chamber is closed from the compressed air underneath bydampers.

Such an apparatus, however, is only usable for the fabrication of hollowbodies made from two different materials and can do nothing to reducethe cycle time of the fabrication procedure and to increase the moldingprocedure per blow pipe and time unit. These and other difficultiesexperienced with the prior art devices have been obviated in a novelmanner by the present invention.

It is, therefore, an outstanding object of this invention to supply theblow pipe with more blank casts in a given time than it is possible withthe known procedure.

With this and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedthereto.

SUMMARY OF THE INVENTION

This invention solves the problem by bringing the blow pipe out of theblow mold into the open before the cooling of the formed hollow body iscompleted. Immediately after removal of the blow pipe from the blowmold, a compressed air-containing member is brought into the blow moldin place of the blow pipe and is kept there until the cooling procedurehas progressed far enough so that the hollow body can be removed fromthe blow mold.

According to a preferred design of the apparatus, introduction of thepressure medium is made with a member leading compressed air into theblow mold even during the removal of the blow pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The character of the invention, however, may be best understood byreference to one of its structural forms, as illustrated by theaccompanying drawings, in which:

FIG. 1 is a side elevational view of a blow-molding apparatus showing itin blowing position,

FIG. 2 is a side elevational view with the mold in position,

FIGS. 3 to 5 are side views of other designs wherein the three drawingsshow three different steps of the fabrication procedure,

FIG. 6 is a plan view of another design of the apparatus, and

FIG. 7 is a vertical sectional view of the apparatus taken on the lineVII--VII of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In a first design of the apparatus with a mold station and a blowingapparatus, the blow pipe and the compressed air-guiding member arearranged on a common guide. In this case, the compressed air-guidingmember can be designed at the same time as a gaging part, which is movedinto the opening of the blow mold after the removal of the blow pipe.

In a second design of this apparatus with one mold and two blowstations, the blow pipe is arranged on a swingable device and themembers guiding the compressed air are designed to be adjustable in thedirection of the opening of one blowing device. The compressedair-guiding member can also be designed in the shape of a rod, which isgenerally the case when an effective purging and with it an effectivecooling is to be achieved. In the drawing, the rod-shaped air-pressureguiding members are shown similar to a blow pipe for the sake ofsimplicity. The rod-shaped compressed air-guiding members are naturallyvery simple and are not comparable to the complicated design of a blowpipe, which also has to be made very accurately and has to be suitablefor the molding procedure and for heat conduction. The invention has theadvantage that the blow pipe, during the relatively long cooling periodof the hollow body, is removed from the blow mold and is moved to a moldstation where another molding may start on the next blank which may beput onto the blow pipe. During this time, the necessary inside pressureis maintained within the blow mold by the compressed air-guiding memberwithout which the cooling procedure cannot proceed because of the memoryeffect. Until the hollow body is cooled within the blow mold, the newblank can already be prepared and waiting, so that, after the exit ofthe cooled-off hollow body, the blow mold is immediately usable. Thetime saving achieved by this procedure may further be increased becauseduring the cooling procedure the new blank attached to the blow pipe,can be moved into another blow mold, so that with a simple blow pipe twoor more blow molds may be served during a single cycle in which the blowpipe normally would be blocked by the continuous procedure, especiallyduring the cooling-off period within the blow mold. If one considersthat the blow pipe and the pre-mold station for the blanks are generallythe most complicated and most expensive tools of a blow-moldingapparatus, a lowering of the costs with a considerable increase ofcapacity can be achieved.

The air-pressure guiding member can be designed in such a way that thecompressed air is introduced into the blow mold before the memberarrives there, that is, immediately after removal of the blow pipe fromthe blow mold. By this method it can be assured that, even in cases inwhich under certain conditions a specially large susceptibility to theappearance of a memory effect is present, it may be prevented. Theair-pressure guiding member can serve at the same time as a gagingdevice which shapes the throat part of the hollow body. In other cases,it may be preferable to hold the rod-shaped air-pressure guiding memberin a certain position above the opening of the hollow mold from whichthe blow pipe was removed. By this method the incoming compressed aircan be used as a purging medium by which a fast cooling of the hollowbody is made possible, especially in the throat part where generally thewall thickness is somewhat larger because no appreciable stretching ofthe material occurs.

FIG. 1 shows a blowing apparatus 2 consisting of the two halves 4 whichmay be moved apart on a parting line extending in the plane of thedrawing. A blow pipe 3 has already expanded the hollow body 7. Throughthe blow pipe 3 and the guide 5 passes a channel 8 for the compressedair. A compressed air-supplying member 3 blows compressed air into thehollow body 7 after removal of the blow pipe 3 from blow mold 2. Thecompressed air-supplying member 3' serves at the same time as a gagethat is brought into the hollow body 7 for shaping its throat. A valve 9in the line leading to the compressed air leading member 3' is kept inits closed position and the valve 10 in the line to the blow pipe 3 iskept in its open position when the blow pipe 3 is expanding the hollowbody 7. When the air-leading member 3' is supplying compressed air, thevalve 10 will be closed and the valve 9 opened. As soon as the blow pipe3 has been removed from the blow mold 2, the guide 5 is brought to theopening of the blow mold far enough so that the compressed air entersthe hollow body 7 from the member 3'. If a gaging of the throat isrequired, then the compressed air-supplying member 3' is lowered intothe throat far enough so that the throat of the hollow body 7 isproperly formed. If a gaging is not necessary, the member 3' may bebell-shaped, so that the lower bell rim fits tightly around the openingwhich is created by the removal of the blow pipe.

A pre-shaping of the blank is shown in FIG. 2. The blow pipe 3 is movedfrom the blow mold 2 into the pre-shape device 1 underneath it. Shownonly in part and in simplified form is an injection-molding device 1'which sprays the material into the pre-shape device 1 and the materialis formed around the blow pipe 3 for a pre-cast, which will be blown upto the hollow body 7 as described in FIG. 1. In FIG. 2 this pre-shapestation as well as the blowing device is formed in two halves which canbe moved away from each other. The injection-molding device 1' can bemoved laterally underneath the pre-forming station may it be swungunderneath.

The pre-forming station shown in FIGS. 3 to 5, is designed to use thedip-blow procedure. The blowing device 2a consists of the two halves 4a,which may be moved apart in the drawing plane. The blow pipe 3a dipsinto the pre-shape station 1a which is designed as a dip station. Thecompressed air-leading member 3'a is rod-shaped and together with theblow pipe 3a is fastened to a common guide 5a which is displaceablewithin the housing 6a. The air passages leading the blow pipe 3a and tothe compressed air-supplying member 3'a are not shown here because oftheir simplicity. They are designed, however, in a manner similar to thedesign shown in FIGS. 1 and 2 and are also equipped with thepreviously-described valves 9 and 10.

In FIG. 3 the blow pipe 3a takes on a pre-cast by dipping. Thereafter,the housing 6a is displaced upwardly along the blow pipe axis, so thatthe blow pipe 3a and with it at the same time the compressedair-supplying member 3'a is pulled out of the dip station 1a.Thereafter, the guide 5a is pulled into the housing 6a so far that theblow pipe 3a may be pushed into the blow device 2a and the housing 6alowered again. Now the pre-cast is blown up and is positioned at theinside contour of the blow device 2a (see FIG. 4). As soon as the hollowbody 7a is sufficiently blown up, the blow pipe 3a and the air-supplyingmember 3'a take the position shown in FIG. 3, which is also shown inFIG. 5. The blow pipe now takes a new pre-cast and the air-pressuresupplying member 3a supplies the hollow body 7a of thepreviously-described operation cycle with compressed air until thehollow body is cooled off. In place of compressed air, the organ 3'a canbe supplied with another gas or pressure media. For example, in thisway, a medium can be used which at the same time can fill the hollowbody.

FIGS. 6 and 7 show a horizontally swingable and vertically adjustableblow pipe 3b and a vertically adjustable air-pressure supplying member3'b for each of the two blow devices 2b. The blow pipe 3b can bedisplaced between the blow devices 2b and the proper air-pressuresupplying members 3'b which are arranged additionally above the blowdevices 2b and always located at the corresponding height. The operationprocedure of this design is as follows: The blow pipe 3b takes on apre-cast in the pre-shape station 1b and the pre-cast is blown up in theleft blow device 2b. After sufficient blowing, it will leave the blowstation 2b and the compressed air-supplying member 3b located above theblow mold moves into the blow device and completes the blow-and-coolingprocess. During this time, the blow pipe 3'b is already taking on a newpre-cast from the pre-shape station 1b, so as to bring it into the rightblow device 2b and to blow it up there as far as necessary. Thereafter,the blow pipe 3b moves back to its pre-cast station 1 and the propercompressed air-supplying member 3'b completes the blow-and-coolingprocess. With this design, therefore, only one precision-fabricated andprecision-working blow pipe 3b is required for one pre-shape station 1and two blow devices 2, since each blow device has its own verticallyadjustable, air-pressure supplying member, which completes theblow-and-cooling process during each cycle.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:.]. .Iadd.I claim:.Iaddend. 1.Blow-molding apparatus for the fabrication of a hollow body ofthermoplastic material within a blow mold, the body being subsequentlyreleased from the mold, comprising:a. a conventional blow pipe (3)capable of providing a first stream of gas, b. a guide (5) forselectively implanting the blow pipe into the mold and extracting theblow pipe from the mold before the body is released from the mold, c. agas-supplying member of simple construction (3') .[.mounted on the guideand.]. separate from the blow pipe, the member being capable ofsupplying a second stream of gas to the mold after the removal of theblow pipe, .[.the guiding serving to move.]. the said member .Iadd.beingmovable .Iaddend.into and out of the mold, and d. a valve system (9,10)for selectively directing gas to the blow pipe (3) and the member (3'),the blow pipe expanding the body of thermoplastic within the mold andthe gas-supplying member maintaining a positive gas pressure within thebody while it is allowed to cool.
 2. Blow-molding apparatus as recitedin claim 1,characterized by the fact that the supplying of compressedgas to the gas-supplying member (3') takes place during a removal of theblow pipe (3) from the blow mold (2).
 3. Blow-molding apparatus asrecited in claim 1,characterized by the fact that a pre-cast station (1)and the common guide (5) are provided and the pre-cast station (1) andthe blow mold (2) are located so that the blow pipe (3) and thecompressed gas-supplying member (3') are arranged on the common guide(5) and extend in a single direction from the common guide (5). 4.Blow-molding apparatus as recited in claim 3, characterized by the factthat the blow mold is provided with an opening, the gas-supplying member(3') is shaped to act as a gaging part and, after removal of the blowpipe (3), the member is moved into the opening in the blow mold (2). 5.Blow-molding apparatus as recited in claim 1,characterized by the factthat one pre-shape station (1b) and two blow molds (2) are provided andthe blow pipe (3b) is arranged on a swingable device, while a separategas-supplying member (3'b) is mounted for movement into and out of eachof the blow molds (2b).
 6. Blow-molding apparatus as recited in claim1,characterized by the fact that the gas-supplying member (3') is rodshaped.